1. Field of the Invention
The present invention relates to a transparent laminate, a method for producing the transparent laminate, and a plasma display panel (hereinafter referred to as “PDP”) filter using the transparent laminate.
The present application is based on Japanese Patent Applications No. Hei. 11-369355 and 2000-383072, which are incorporated herein by reference.
2. Description of the Related Art
Nowadays in the society where information orientation is advancing remarkably, performance required of a display to be used as a terminal for displaying an image is diversified greatly. Especially, a great deal of attention has been paid to a PDP as a novel display succeeding a CRT and a liquid-crystal display because it is easy to increase the size of the PDP while reducing the thickness of the PDP. The PDP has already come onto the market.
In the PDP, electric discharge is produced in rare gas enclosed in the panel, especially, in gas containing neon as a main component. R, G and B fluorescent materials applied onto cells of the panel are made to emit fluorescence by vacuum ultraviolet rays generated at the electric discharge. In this light emission process, electromagnetic waves and near-infrared rays unnecessary for display on the PDP are emitted simultaneously. The electromagnetic waves need to be cut because they cause malfunctions of peripheral devices and have bad influence on human bodies. The near-infrared rays also need to be cut because there is a problem that remote controllers of household electronic appliances, karaoke, audio-video systems, etc. are made to malfunction by the near-infrared rays because the near-infrared rays have a wave range of from 850 to 1200 nm whereas the remote controllers have a light-receiving sensitivity range of from 700 to 1300 nm.
In a transparent laminate of the type having a structure in which a metal thin film is sandwiched between high-refractive-index transparent thin films, both the electrically conducting property and infrared reflecting property of the metal thin film can be utilized and, at the same time, a function of preventing reflection of visible rays on a metal surface of the metal thin film can be given to the transparent laminate by the high-refractive-index transparent thin films. Accordingly, such a transparent laminate is adapted to materials capable of transmitting visible rays but reflecting heat rays, such as a transparent heat-insulating material for solar cell, a window material for agricultural green house or building, a food showcase, etc. Further, the transparent laminate exhibits transparency and high electrical conductivity. Accordingly, such a transparent laminate is also adapted to materials such as liquid-crystal display electrodes, electric field light-emitting material electrodes, electromagnetic wave shielding films, anti-static films, etc. The structure of such a transparent laminate has been described in JP-A-55-11804, JP-A-9-176837, etc.
However, the aforementioned transparent laminate did not have performance permitting direct use as a PDP filter and, hence, it was unable to satisfy both high electromagnetic wave shielding property and near-infrared cutting property simultaneously. In use as a PDP filter, visible light transmitting property to prevent the display quality of the PDP from being spoiled is required intensively in addition to the aforementioned two properties. Especially, setting the color tone of the filter to neutral gray is required intensively. Anti-reflection property is further required from the point of view of prevention of mirroring of external light, light emitted from a fluorescent lamp, or the like. It was, however, impossible that these requirements were served by the aforementioned transparent laminate.
Particularly to set the color tone of the PDP filter to neutral gray, it is necessary that the transmittance of the PDP filter is kept constant in a visible light range or the transmittance of each wavelength is adjusted to make the color tone neutral gray. In the transparent laminate having a metal thin film sandwiched between high-refractive-index transparent thin films, it was not easy to keep the transmittance constant all over the visible light range. For example, an effort was made at adjusting the color tone to neutral gray by adding and uniformly dispersing a dye, or the like, capable of absorbing light with a specific wavelength into the transparent substrate, or the like. It was, however, not easy to adjust finely the respective amounts of a plurality of absorbents to be added and disperse uniformly the absorbents. Hence, there was a problem that a greater part of absorbents lacked durability as well as a high-grade technique was required.